import katex from '../katex.mjs';

/* eslint no-constant-condition:0 */
const findEndOfMath = function findEndOfMath(delimiter, text, startIndex) {
    // Adapted from
    // https://github.com/Khan/perseus/blob/master/src/perseus-markdown.jsx
    let index = startIndex;
    let braceLevel = 0;
    const delimLength = delimiter.length;

    while (index < text.length) {
        const character = text[index];

        if (braceLevel <= 0 && text.slice(index, index + delimLength) === delimiter) {
            return index;
        } else if (character === "\\") {
            index++;
        } else if (character === "{") {
            braceLevel++;
        } else if (character === "}") {
            braceLevel--;
        }

        index++;
    }

    return -1;
};

const splitAtDelimiters = function splitAtDelimiters(startData, leftDelim, rightDelim, display) {
    const finalData = [];

    for (let i = 0; i < startData.length; i++) {
        if (startData[i].type === "text") {
            const text = startData[i].data;
            let lookingForLeft = true;
            let currIndex = 0;
            let nextIndex;
            nextIndex = text.indexOf(leftDelim);

            if (nextIndex !== -1) {
                currIndex = nextIndex;
                finalData.push({
                    type: "text",
                    data: text.slice(0, currIndex)
                });
                lookingForLeft = false;
            }

            while (true) {
                if (lookingForLeft) {
                    nextIndex = text.indexOf(leftDelim, currIndex);

                    if (nextIndex === -1) {
                        break;
                    }

                    finalData.push({
                        type: "text",
                        data: text.slice(currIndex, nextIndex)
                    });
                    currIndex = nextIndex;
                } else {
                    nextIndex = findEndOfMath(rightDelim, text, currIndex + leftDelim.length);

                    if (nextIndex === -1) {
                        break;
                    }

                    finalData.push({
                        type: "math",
                        data: text.slice(currIndex + leftDelim.length, nextIndex),
                        rawData: text.slice(currIndex, nextIndex + rightDelim.length),
                        display: display
                    });
                    currIndex = nextIndex + rightDelim.length;
                }

                lookingForLeft = !lookingForLeft;
            }

            finalData.push({
                type: "text",
                data: text.slice(currIndex)
            });
        } else {
            finalData.push(startData[i]);
        }
    }

    return finalData;
};

/* eslint no-console:0 */

const splitWithDelimiters = function splitWithDelimiters(text, delimiters) {
    let data = [{
        type: "text",
        data: text
    }];

    for (let i = 0; i < delimiters.length; i++) {
        const delimiter = delimiters[i];
        data = splitAtDelimiters(data, delimiter.left, delimiter.right, delimiter.display || false);
    }

    return data;
};
/* Note: optionsCopy is mutated by this method. If it is ever exposed in the
 * API, we should copy it before mutating.
 */


const renderMathInText = function renderMathInText(text, optionsCopy) {
    const data = splitWithDelimiters(text, optionsCopy.delimiters);
    const fragment = document.createDocumentFragment();

    for (let i = 0; i < data.length; i++) {
        if (data[i].type === "text") {
            fragment.appendChild(document.createTextNode(data[i].data));
        } else {
            const span = document.createElement("span");
            let math = data[i].data; // Override any display mode defined in the settings with that
            // defined by the text itself

            optionsCopy.displayMode = data[i].display;

            try {
                if (optionsCopy.preProcess) {
                    math = optionsCopy.preProcess(math);
                }

                katex.render(math, span, optionsCopy);
            } catch (e) {
                if (!(e instanceof katex.ParseError)) {
                    throw e;
                }

                optionsCopy.errorCallback("KaTeX auto-render: Failed to parse `" + data[i].data + "` with ", e);
                fragment.appendChild(document.createTextNode(data[i].rawData));
                continue;
            }

            fragment.appendChild(span);
        }
    }

    return fragment;
};

const renderElem = function renderElem(elem, optionsCopy) {
    for (let i = 0; i < elem.childNodes.length; i++) {
        const childNode = elem.childNodes[i];

        if (childNode.nodeType === 3) {
            // Text node
            const frag = renderMathInText(childNode.textContent, optionsCopy);
            i += frag.childNodes.length - 1;
            elem.replaceChild(frag, childNode);
        } else if (childNode.nodeType === 1) {
            // Element node
            const className = ' ' + childNode.className + ' ';
            const shouldRender = optionsCopy.ignoredTags.indexOf(childNode.nodeName.toLowerCase()) === -1 && optionsCopy.ignoredClasses.every(x => className.indexOf(' ' + x + ' ') === -1);

            if (shouldRender) {
                renderElem(childNode, optionsCopy);
            }
        } // Otherwise, it's something else, and ignore it.

    }
};

const renderMathInElement = function renderMathInElement(elem, options) {
    if (!elem) {
        throw new Error("No element provided to render");
    }

    const optionsCopy = {}; // Object.assign(optionsCopy, option)

    for (const option in options) {
        if (options.hasOwnProperty(option)) {
            optionsCopy[option] = options[option];
        }
    } // default options


    optionsCopy.delimiters = optionsCopy.delimiters || [{
        left: "$$",
        right: "$$",
        display: true
    }, {
        left: "\\(",
        right: "\\)",
        display: false
    }, // LaTeX uses $…$, but it ruins the display of normal `$` in text:
        // {left: "$", right: "$", display: false},
        //  \[…\] must come last in this array. Otherwise, renderMathInElement
        //  will search for \[ before it searches for $$ or  \(
        // That makes it susceptible to finding a \\[0.3em] row delimiter and
        // treating it as if it were the start of a KaTeX math zone.
        {
            left: "\\[",
            right: "\\]",
            display: true
        }];
    optionsCopy.ignoredTags = optionsCopy.ignoredTags || ["script", "noscript", "style", "textarea", "pre", "code"];
    optionsCopy.ignoredClasses = optionsCopy.ignoredClasses || [];
    optionsCopy.errorCallback = optionsCopy.errorCallback || console.error; // Enable sharing of global macros defined via `\gdef` between different
    // math elements within a single call to `renderMathInElement`.

    optionsCopy.macros = optionsCopy.macros || {};
    renderElem(elem, optionsCopy);
};

export default renderMathInElement;
